The continuous and rapid increase of areal density in magnetic data storage systems required a continuous increase of the coercivity of the storage media. In order to be able to record on these everhigher-coercivity media, new soft magnetic materials for pole tips with increased magnetic moment had to be developed. Significant progress has been made during the last few years in electroplating alloys with high saturation magnetic flux density for use in writing heads. We review recent progress made in this area, with particular emphasis on the work done at IBM since the review paper on the subject was published in this journal in 1998 by Andricacos and Robertson. Reviewed here are the high-moment alloys of NiFe, particularly in the very high iron range [an extension of permalloy (Ni 80 Fe 20) and Ni 45 Fe 55 ]; very-high-cobalt CoFeCu alloys; ternary CoNiFe; and binary iron-rich CoFe alloys. With the latter binary alloy films, we have demonstrated that it is possible to reach by electroplating the saturation flux density limit of 2.4-2.5 T reported for cast alloys. Since the electroplating of good-magneticquality iron-rich CoFe alloys posed a considerable challenge, the behavior of the CoFe plating system was studied in detail, using in situ surface pH measurements and a rotating-cylinder Hull cell.
Plated high saturation magnetization soft magnetic FeCo films were annealed in magnetic field; their stress, microstructure, and magnetic properties were investigated. The FeCo films consistently showed a reduced tensile stress after magnetic annealing at temperatures above 255°C. The annealing temperature was found to be the primary factor in reducing the tensile stress, while annealing time was secondary. The FeCo films showed improved soft magnetic properties when subjected to an easy axis annealing with reduced coercivities along both the easy axis and hard axis. Hard axis annealing on these FeCo films caused a switched easy and hard axis in these films when the annealing temperature is above 255°C.
Studies were carried out on the laminated structures FeCo/Cu and FeCo/Ru prepared by two-bath plating, one-bath plating and plating-sputtering hybrid method. Zero remnant magnetization as in antiferromagnetically coupled structures made by sputtering was not achieved. A slow magnetization was observed for structures plated from two baths. A hypothesized mechanism was proposed, involving a superparamagnetic component due to the displacement and corrosion reactions. This effect is less prominent in the structures prepared with one bath plating. Lower magnetic moments were observed, probably due to the inclusion of Cu in FeCo layers as well as a displacement reaction. All the structures prepared by plating-sputtering method behave like a bulk ferromagnetic material. An increase and decrease of the magnetic moment was observed for FeCo/Cu and FeCo/Ru, respectively, probably due to the different effect on the corrosion reaction by Cu and Ru.
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